In the processing of tungsten ores, concentrates and scraps to pure tungsten chemicals, the source material is first digested with sodium hydroxide or sodium carbonate to yield an impure sodium tungstate solution. In this digestion, other elements such as arsenic, phosphorus, silicon, tin, etc., are also solubilized.
It has been common practice to remove arsenic and phosphorus from this impure sodium tungstate solution by formation of sparingle soluble salts as magnesium ammonium arsenate and magnesium ammonium phosphate. Because of the pH conditions of this removal step, silicon is simultaneously removed from the solution. However, tin is not reliably removed in this or in any other subsequent treatment step. Most of the tin which is solubilized in the initial digestion process remain with the final tungsten product when existing purification methods are employed.
Therefore, a method to effectively remove tin from the impure sodium tungstate solution would be desirable.